Method and system for controlling the temperature of a heat measuring sensor especially in motor vehicles

ABSTRACT

A method and system for controlling the temperature of a heat measuring sensor such as an oxygen sensor located in the exhaust line of an internal combustion engine so that the oxygen sensor will operate within optimal operating temperature. To accomplish this, a heating system including a control mechanism is provided for the oxygen sensor which adjusts the temperature of the oxygen sensor by controlling the output of a heater during the operation of the internal combustion engine according to characteristic engine operating conditions which have an effect on the temperature of the oxygen sensor, the most significant of which is engine load status. These conditions are sensed as a quantity by probes located so as to measure such operating conditions and send a signal to the control mechanism and its sensor heater.

This is a continuation, of application Ser. No. 924,407 filed July 13,1978, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to heat sensors for installation in motorvehicles.

The prior art temperature measuring sensors for measuring the exhausttemperature for automotive vehicles utilized the internal resistance ofthe heat sensor itself to supply a signal representing the measuredtemperature since the conductivity of the sensor was extremelytemperature-dependent. However, the disadvantage of this type of sensorwas the expense involved to sense the change in conductivity of theinternal resistance and the possible counter-influence of the sensor'smeasurement signal and the interior resistance measurement. Thissometimes required an interruption of the current to insure that thecorrect measurement signal was being sent. Further, while it is known toinclude supplementary temperature probes within the measuring sensoritself and thus measure the temperature sensor with no intermediarydevice. It has also been found that this latter type of temperaturemeasurement is very costly and, at present, the life expectance of themeasuring sensor is much shorter than that of the temperature probes andthus the device must be replaced often.

OBJECT AND SUMMARY OF THE INVENTION

Accordingly it is a primary object of this invention to provide a methodand system of the above-described type wherein the heat measuring sensorfor measuring the exhaust line temperature of an internal combustionengine is maintained at its optimal operating temperature.

It is another object of this invention to provide a method and system ofthe above-described type which has the advantages that the measurementsensor circuit need not be interrupted or supplementary elements neednot be included within the measuring sensor.

These objects are obtained according to the invention by adjusting thetemperature of the oxygen sensor to its optimal operating temperatureaccording to the characteristic operating quantities of the internalcombustion engine which have a significant influence over the sensortemperature, the most significant of which is the load status of theengine.

Thus, a more particular object of the invention is to use the loadstatus of the internal combustion engine to adjust the measuring sensortemperature.

The invention will be better understood as well as further objects andadvantages thereof will become more apparent from the following detaileddescription of the exemplary embodiments taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the temperature of exhaust gas with respect tothe operational load status of an internal combustion engine;

FIGS. 2a and 2b show two simplified schematic wiring diagrams of asensor heating system;

FIG. 3a shows a control installation for a sensor heating system indetail and FIG. 3b is a graph showing the relationship of input voltageand output current for the sensor heater;

FIG. 4a shows a control installation for the heating system which isdependent on the angle of a throttle valve, and FIG. 4b is a graphshowing the relationship between throttle valve angle and sensor heateroutput; and

FIG. 5 is a schematic illustration of a control installation which isactuated by the intake pressure and/or the exhaust gas pressure ininternal combustion engines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the relationship between the engine load and the exhaustgas temperature in internal combustion engines. The significanttemperatures shown are 200° C. at engine idling speed, approximately400° C. in the mid-range of partial engine loading, and almost 800° C.at full engine load. The dotted horizontal line marking the temperatureof about 680° C. indicates the optimal operating temperature of anoxygen measuring sensor. It can be seen from the curve that this optimaloperating temperature of the oxygen sensor is first reached in the upperpartial-load range, while under idling and lower partial-load conditionsparticularly in V-engines, the exhaust gas temperature at the pointwhere a sensor could be installed is too low. The provision for aheating system for such a sensor which is adjustable according to engineload is therefore clearly needed.

FIG. 2a shows a simplified schematic wiring diagram of an oxygen sensorheating system installation. A heating element 10 is supplied with heatenergy by means of a potentiometer 13 situated between a positive lead11 and a negative lead 12. The control mechanism for the sensor heateris identified as 15 and it is equipped to receive, as for example,inputs for rpm, throttle valve angle and pressure rate of air flow inintake manifold and temperature. The control mechanism 15 produces anoutput voltage UR characterizing the particular temperature of themeasuring sensor at the moment, which operates the potentiometer 13through a switch means shown as block diagram at 16.

As to the installation of the invention, the indicated input quantitiesfor the control mechanism 15 are given only as examples and need not allbe utilized since the utilization of the load status alone is sufficientfor temperature adjustment as may be seen in FIG. 1. By rpm herein ismeant camshaft revolutions although the distributor shaft revolution mayalso be used, both of which are much lower in number at idling speedthan in the full-load range. Too, the throttle valve angle α, or thepressure on the air flow rate in the intake manifold may also beutilized alone as an input to the control mechanism and the pressuresignal P can be taken either at the intake side or the exhaust side ofthe engine. These locations may be selected because, as is well known,at idling speed there is a vacuum in the intake manifold and also asmall pressure on the exhaust side of the engine, but at full load theamount of vacuum in the intake manifold is reduced and the pressure atthe exhaust side is increased. However, in each installation of theinvention it must be noted which location is chosen and the controlmechanism 15 adjusted accordingly, and it is important to point out thata position near the sensor may be selected for temperature measurementby the probe, or a convenient point in the exhaust line may equally wellbe employed since the time delay involved is insignificant. It is,however, significant that temperature jumps of 250° per second can ariseon the exhaust side of the internal combustion engine and for thisreason a certain distance between exhaust valves and temperature sensoris practical.

FIG. 2b shows a modification of the embodiment shown in FIG. 2a, wherethe control voltage UR is directed to a voltage-pulse width converter18, which generates pulses t_(i) that activate a switch 19, instead ofpotentiometer 13 of FIG. 2a, situated in the circuit of the heatingelement 10.

FIG. 3a shows a detailed control installation with the heating element10 and a transistorized emitter-follower circuit connected thereto toprovide current IH for the heater 10. The input of the emitter-follower20 is connected by a resistor 21 with a positive lead 22, as well aswith the output of an inverse feedback circuit to differential amplifier24. The positive input of the amplifier 24 is connected with a negativelead 26 through a resistor 25 while the negative input receives theinput signal UE from input node 28 through input resistor 29. Theinverse feedback resistor is identified as 30.

FIG. 3b shows the relationship between input voltage UE of the switchingarrangement as in FIG. 3a and the current IH through heating element 10depending upon the relationship of the selected resistance values forresistors 29 and 30 when wiring the amplifier 24 in the circuit as shownin FIG. 3a.

FIG. 4a shows an installation for oxygen sensor heating which isdependent in three states or steps of the throttle valve angle α forsupplying current to the heating element 10. The throttle valve is shownhere schematically as swivel arm 40 revolving about a pivotal axis 41.The swivel arm 40 is connected to a positive lead 42 and moves throughrelatively small angles making contact with two contact surfaces 43 and44, which are connected with the heating element 10 through twodifferent resistors 45 and 46. The contact surface 43 is situated in theidling range LL and thus is engaged at small throttle valve angles; thecontact surface 44 is situated in the partial-load range TL and engagedat medium throttle valve angles; while the full-load range VL is givenwith large throttle valve angles, in which case there is no contactsurface current supplied to the heating element.

FIG. 4b is a graph showing angles of the throttle valve in relation toheat generated by the heating system used with the arrangement shown inFIG. 4a. It can be seen that the heat generated by the heater 10 isstairstep in nature, and that in the idling range up to about a 30°throttle valve angle, LL in FIG. 4a, the maximum heating capacity of theheating element 10 is available, and is in the partial-load rangebetween throttle valve angles of 30° and 60°, TL in FIG. 4a, half of theheating capacity is available, while in the full-load range at throttlevalve angles between 60° and 90°, VL in FIG. 4a, there is no provisionfor heating the measuring sensor. The abscissa of the graph in FIG. 4bshows both an angle measurement scale and a pressure measurement scaleP/mm Hg which symbolizes the pressure-dependent control of the heatingsystem.

FIG. 5 finally shows a simplified schematic arrangement for apressure-dependent control of the heating system. Again a three-stageheating control is provided as in the arrangement in FIG. 4a, but inthis embodiment, the contact surfaces 43 and 44 are no longer engaged bya swivel arm but by a slider 51 which is actuated by a pressureconverter 50. Input quantities of the pressure converter 50 may beeither the pressure in the induction manifold 52 or as indicated by adotted line by the pressure on the output side in the exhaust line 53 ofthe internal combustion engine. Contact pads which the slider 51engages, are again connected to resistors 54 and 56. Thus, the heatingcapacity of heating element 10 is determined so that the highest heatproduction is achieved at idling speeds and none at full load as in FIG.4a.

In addition to the control arrangements suggested above for the heatcapacity of heating elements for measuring sensors, it is possible,where internal combustion machines in motor vehicles have continuouslyoperating injection systems, to use the control pressure in the fuelcircuit or the fuel adjustment circuit as the control value for theheating capacity.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other embodiments and variantsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A temperature control for a measuring sensorlocated in the exhaust gas line of an internal combustion engine of anautomotive vehicle comprising:a measuring means, a heating element forcontrolling the temperature of said measuring means; a plurality ofcontrol mechanisms including said measuring means for measuring acontrol quantity and being selectively coupled in series with saidheating element for determining at least three ranges including avariable heating performance at least at idling range and atpartial-load range; means selecting one of said plurality of saidcontrol mechanisms including said measuring means, said selecting meansselecting a selected characteristic operating quantity of said engineload including air flow rate measurement connecting one of said selectedcontrol mechanisms to said heating element for controlling the variableheat output of said heating element according to the measured quantityin at least two of said ranges, said automotive vehicle including athrottle valve rotatably fixed to move in an arc by a vehicle operator;means responsive to the position of said throttle valve to provide astepped signal output; and means for receiving said stepped signaloutput to vary the heat output of said heating element.
 2. Thetemperature control as claimed in claim 1, wherein the characteristicoperating quantities of said internal combustion engine furthercomprises: the pressure in the exhaust manifold, the pressure in theexhaust line, the revolutions per minute of its camshaft, therevolutions per minute of its distributor shaft, the pressure in itsintake manifold, the air flow rate in its intake manifold, thetemperature in its exhaust line, andwherein said control mechanismincludes at least one sensor probe to measure at least one saidoperating quantity.
 3. The temperature control mechanism as claimed inclaim 1, wherein said means for measuring said quantity includes a probefor measuring the pressure in the intake manifold.
 4. The temperaturecontrol mechanism as claimed in claim 1, wherein said means formeasuring said quantity includes a probe for measuring the air flow ratein said intake manifold.
 5. The temperature control as claimed in claim1, wherein said means for measuring said quantity includes means formeasuring the temperature in the exhaust line.
 6. The temperaturecontrol as claimed in claim 1, wherein said control mechanism includes avoltage responsive converter responsive to said measuringmeans;switching means connected to said voltage responsive converterwhich opens and closes in response to the voltage output from saidconverter.
 7. A temperature control for a measuring sensor located inthe exhaust gas line of an internal combustion engine of an automotivevehicle comprising:a measuring means, a heating element for controllingthe temperature of said measuring means; a plurality of controlmechanisms including said measuring means for measuring a controlquantity and being selectively coupled in series with said heatingelement for determining at least three ranges including a variableheating performance at least at idling range and at partial-load range;means selecting one of said plurality of said control mechanismsincluding said measuring means, said selecting means selecting aselected characteristic operating quantity of said engine load includingair flow rate measurement connecting one of said selected controlmechanisms to said heating element for controlling the variable heatoutput of said heating element according to the measured quantity in atleast two of said ranges, said control mechanism including adifferential amplifier having a negative input and a positive input,said negative input being connected to the output from said measuringmeans and said positive input being connected to vehicle ground; atransistorized emitter-follower connected to the output of saiddifferential amplifier; and the input of said emitter-follower connectedto the output of said differential amplifier; the output of saidemitter-follower being connected to said heating element whereby thecurrent from said heating element is directly responsive to the voltageapplied to the negative input of said differential amplifier.
 8. Thetemperature control as claimed in claim 7, wherein a resistance means iscoupled between said measuring means and said negative input of saiddifferential amplifier, a second resistance means is located betweenvehicle ground and the positive input to said differential amplifier tovary the operating characteristics of said control mechanism.
 9. Atemperature control for a measuring sensor located in the exhaust gasline of an internal combustion engine of an automotive vehiclecomprising:a measuring means, a heating element for controlling thetemperature of said measuring means; a plurality of control mechanismsincluding said measuring means for measuring a control quantity andbeing selectively coupled in series with said heating element fordetermining at least three ranges including a variable heatingperformance at least at idling range and at partial-load range; meansselecting one of said plurality of said control mechanisms includingsaid measuring means, said selecting means selecting a selectedcharacteristic operating quantity of said engine load including air flowrate measurement connecting one of said selected control mechanisms tosaid heating element for controlling the variable heat output of saidheating element according to the measured quantity in at least two ofsaid ranges, said control mechanism including a pressure responsiveslide mechanism, said measuring means being connected to a source ofpressure in said internal combustion engine, said slide mechanism beingmovable in response to the pressure measured by said measuring means,said slide mechanism also being connected to a source of positivevoltage, a plurality of conductor pads and resistance means, oneresistance means of a different value for each conductor pad and eachconnected in series with said heating element and vehicle ground, saidslide mechanism including means for engaging said conductor pads one ata time for connecting said positive voltage source with said heatingelement and vehicle ground to vary the output of said heating element.10. A temperature control for a measuring sensor located in the exhaustgas line of an internal combustion engine of an automotive vehiclecomprising:a measuring means, a heating element for controlling thetemperature of said measuring means, at least one control mechanismincluding said measuring means for measuring a control quantity andbeing selectively coupled in series with said heating element fordetermining at least one range including a variable heating performanceat least at idling range, means selecting said at least one controlmechanism including said measuring means, said selecting means selectinga selected characteristic operating quantity of said engine loadincluding air flow rate measurement connecting said means selecting saidat least one control mechanism to said heating element for controllingthe variable heat output of said heating element according to themeasured quantity in at least at idling range, means rotatably fixed tomove in an arc by a vehicle operator, means responsive to the positionof said rotatably fixed means to provide a stepped signal output, andmeans for receiving said stepped signal output to vary the heat outputof said heating element.